The present invention relates generally to an apparatus incorporating driving motors disposed in a common housing and more specifically to hermetic motor compressor assemblies.
Many types of machines incorporate a driving motor disposed in a housing which housing also encloses the apparatus being driven by the motor. Hermetic motor compressors are typical of such machines. In the case of most reciprocating compressor designs, the motor stator is usually mounted directly to the cylinder block, as is desirable with the conventional internal spring mounting arrangement of the cylinder block used in such compressors. In the case of scroll (or rotary) compressor designs, where spring-mounting of the compression members is not required, a simplified and more economical method can be employed. For these cases, the motor is usually mounted by press fit directly into the compressor shell, thereby requiring the size of the motor stator laminations outer diameter to coincide with the size of the compressor shell.
In the design of scroll compressors for particular applications, it may be desirable to allow the size of the compressor shell to depart from the frame size of the motor stator, allowing geometrical optimization of both members to occur independent of the other. In the case where the desired compressor shell size is larger than the size of the desired motor stator frame, the need arises to arrive at a convenient method of mounting the motor stator, so as to avoid the economical disadvantages of added cast iron housings, mounting fasteners, and the like. While it is possible to provide a shell having a first portion of one diameter to accommodate the compressor and another portion of a different diameter to accommodate the motor stator, such stepped type shells are more costly to fabricate than conventional cylindrical shells.
In applications in which the motor stator diameter is less than the compressor diameter it is possible to incorporate an intermediate sleeve member having an inside diameter that adapted to receive the motor stator in a press fit relationship and an outside diameter adapted to receive the compressor outer shell in a press fit relationship. In the case where the difference in size between the motor stator and the compressor shell is large, the primary problem faced with this approach is damage (buckling) to the motor stator laminations, due to the extreme stiffness created by the thickness of the sleeve. In such cases, all the stress present from the press fit is affected primarily normal to the stator lamination outside diameter. This problem is greatly magnified if a cold press-fit technique (most economical) is employed, as the stress of the press fit between the parts must be initially supported solely by the first (several) lamination(s) in the stack, during the initial entry of the press fit.
The present invention overcomes these problems by providing a flexible sleeve which flexes when subjected to the forces from the press fit of the motor stator and the compressor shell, while transmitting enough normal force to "grip" between the compressor shell and the motor stator, thereby effectively supporting the motor and the torque generated thereby. The more flexible the sleeve can be designed, the less strict control of size is permitted in the manufacture of the stator laminations and the compressor shell.
In a preferred embodiment, the sleeve is in the form of an irregular or multilobed cylinder in which a plurality of radially inner surfaces are provided which engage the stator and a plurality of radially outer surfaces engage the outer shell and are circumferentially offset from the radially inner surfaces. By selection of the size, material and wall thickness, the retaining forces exerted on both the stator and shell can be controlled to ensure adequate holding power while still enabling efficient press fit assembly of the components.